ARC: [plat-hsdk] Add PCIe support

Add PCI support to the ARC HSDK platform allowing to use the generic PCI
setup functions.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>